A team password is optional. If your captain set one, anyone joining the team has to enter it.
Changing the password
The Team Captain can change it at any point.
Make sure you are logged in to Race Space.
Go to My Teams in the main menu.
Select Manage Team.
Select Team Settings.
Select Change Password.
If you have forgotten the password
The quickest way to find out what your current password is, is to send yourself an invite. The invitation email contains it.
Make sure you are logged in, go to My Teams in the main menu and select Manage Team.
Select Email Invite and put your own email address into the invitation.
Open the email you receive. The password is in it.
If you are not the Team Captain, ask your captain to send you an invite or to tell you the password directly.